8: Spectroscopy
- Page ID
- 163000
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Lab Overview
Lab Goals
As a result of this lab, you should be able to:
- Record spectral lines from known sources
- Use spectral patterns to identify mystery gases
- Explain the cause of spectral lines by referencing atomic energy levels
Equipment and Setup
This lab requires the following equipment on each table.
- Spectrum Tube Power Supply
- Spectrum Analyzers
- Spectrum Keys
- Spectrum Tubes containing:
- Hydrogen
- Helium
- 3-4 other gases
Submission Instructions
Submit a brief lab report that includes the following sections:
Methods
Describe the lab setup and the process that you used throughout the different parts of the lab. Include both written explanations and visuals/diagrams. Add a short description of your diagrams after each figure caption.
Results
Include measured spectra, spectrum keys (when relevant) and predicted spectra.
Discussion
Write clear paragraphs that answer the discussion questions throughout the lab.When relevant, be sure to cite evidence from the results section and explain how that evidence supports your claims.
Part 1: Observing Gas Spectra from Known Sources
Background Information
When energized, gases emit light at specific, discrete wavelengths. These result in emission spectrum lines that are unique to each gas, based on the energy levels present in the electron orbital structure of the element/molecule. Molecules are more complex because they also have energy levels based on vibrational modes.
Hydrogen and Helium
- Start with a Hydrogen Spectrum Tube set in the power supply, turn the power supply on:
- Observe the spectrum tube using the Spectrum Analyzer.
- Draw a line at the measured location for each line you see through the spectrum analyzer
- Color your lines to match (approximate) the color of the spectral line.
- Color the tube graphic to match the (approximate) color of the spectrum tube when observed with the naked eye.
- Turn off the power supply and ask your instructor to remove the spectrum tube (they get very hot!). It should be replaced with a Helium Spectrum Tube. Then, repeat steps a-d above.
Discussion Questions:
- Do different gases have the same or different spectral lines?
Part 2: Applying Known Spectra to Unknown Sources
Simplified Solar Spectrum
Lines are drawn for a simplified solar spectrum. Using your key for Hydrogen and Helium, complete the following:
- Identify any lines on the solar spectrum that match the lines on the hydrogen or helium spectrum.
- Label lines that match as either Hydrogen or Helium. It is possible some lines will not match either
- Color the hydrogen/helium lines to match the color of those spectra
- Write a few sentences stating the lines that matched and the unmatched lines
Discussion Questions:
- Is the sun made out of hydrogen? Helium? Both? Neither? Make a claim and support it with evidence.
Predicted Complete Solar Spectrum
If an element is present in the atmosphere of the sun, all of that element’s lines are likely present. Identify any lines on the solar spectrum that match the lines on the hydrogen or helium spectrum.
- Based on the simplified solar spectrum, draw in all of the spectral lines you predict should be present on the sun.
- Label lines that match as either Hydrogen or Helium.
- Color the hydrogen/helium lines to match the color of those spectra
Explanation
Explain your reasoning for the prediction you made about the solar spectrum.
Identifying Mystery Gases
Scientists have followed a similar process to what you did for Hydrogen and Helium to record spectra of different elements. A key for several gases is provided to each table. Additionally, each there are cutouts of each individual gas spectra for use in this lab.
- Obtain a mystery spectrum tube and record the spectrum number on your writeup.
- Observe the mystery gas through the analyzer and record its spectrum on your paper. Include color.
- Use the keys to identify the mystery gas. Tape/glue the key below your recorded spectrum to show the match
- Repeat for additional mystery gases.
Discussion Questions
- Explain the process for which scientists can identify what a gas is made of using spectrum analyzers.
Part 3: Causes of Spectra
- Open the Hydrogen Spectrum simulation from PHET and click on the Energy Levels Tile: https://phet.colorado.edu/sims/html/models-of-the-hydrogen-atom/latest/models-of-the-hydrogen-atom_all.html
- Show the Spectrometer and select De Broglie Model
- Press the red button on the laser to shine light on the hydrogen atom and start collecting data
- Watch the energy level diagram and identify transitions that are colors of light (visible). You do not need to identify other transitions.
- After some time has passed, record the spectrometer data
Discussion Question
- Explain the causes of spectroscopy and/or any patterns you noticed about spectral lines, energy levels, and atomic orbitals.
Templates
